Examine the densest areas in each country and you’ll find some striking trends: Many were built in the same era for the same reasons, but their current popularity is a far cry from where they began.

In the sprawl of a contemporary North American city, it can be tempting to envy urban Europe for its density. For the most part, historic European cities are far more densely populated—their streets, by comparison, appear to be hives of vibrant activity, with compact but handsome apartments that model healthy, sustainable metropolitan living. But look to the densest urban areas in each European country and you’ll see a more complex, ambivalent picture of how they came to be.

Take, for example, Northern Neukölln, Berlin. Though it’s increasingly seen as a desirable place to live today, for much of its existence this dense quarter was considered a social and aesthetic menace, known for overcrowding, dinginess and a generally poor quality of life. Through the twists and turns of history—and the increasing displacement of the lower-income tenants for which it was mainly built—its tightly packed streets and courtyards have come to be seen as a positive model of urban development, containing the single densest square kilometer in Germany.

And Northern Neukölln certainly isn’t alone. A striking number of its counterparts across the continent have followed the same path, starting as hastily built barracks for rural migrants of the Industrial Revolution and ending up today as places that top the lists of neighborhoods where middle-income urbanites might want to live.

In fact, it’s remarkable how many of the densest parts of European countries share similarities in layout, appearance, and origination. That’s all brought to light through a series of fascinating map images collected by Alasdair Rae, professorial fellow at Sheffield University’s Department of Urban Studies and Planning. The images also make clear why 100 years ago—when these areas were inhabited at even higher capacities than today—architects and planners were so keen to find more spacious, less concentrated models for how to lay out a city.

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Before going further, it pays to pin down exactly what areas we’re talking about. Below is a ranking of the most densely populated square kilometers in 30 European countries. This, to be clear, is a list of the densest area in each country, rather than a simple list of the densest areas in Europe, based on 2011 population data.

Ranking

Country

Neighborhood where densest square kilometer is located

Residents per sq/Km

1

Spain

L’Hospitalet de Llobegrat, Greater Barcelona

53,119

2

France

Goutte D’Or, Paris

52, 218

3

Poland

Nowe Miasto, Sczczecin

32,752

4

Belgium

Saint-Josse-Ten-Noode, Brussels

29,100

5

Greece

Zografos, Athens

28,880

6

Sweden

Southwest Södermalm, Stockholm

26,120

7

Bulgaria

Belite Brezi, Sofia

23,934

8

The Netherlands

De Pijp, Amsterdam

23,485

9

Germany

Northern Neukölln, Berlin

23,379

10

Czech Republic

Žižkov, Prague

23,249

11

Denmark

Vesterbro, Copenhagen

22,381

12

Italy

Pendino, Naples

22,113

13

Portugal

Arroios, Lisbon

21,823

14

Switzerland

Grottes Saint Gervais, Geneva

21,456

15

England

Maida Vale, London

20,477

16

Romania

Piața Centrala area, Galați

19,179

17

Estonia

Haabersti, Tallinn

17,375

18

Lithuania

Justiniškės, Vilnius

16,166

19

Norway

Grünerløkka, Oslo

15,673

20

Slovakia

Grunt, Košice

15,379

21

Finland

Punavuori, Helsinki

14,933

22

Ireland

The Liberties, Dublin

12,176

23

Malta

Fgura

11,421

24

Slovenia

Moste/Golovec, Ljubljana

10,504

25

Hungary

District 8, Budapest

10,451

26

Croatia

District 3, Split

10,202

27

Latvia

Avoti, Riga

10,123

28

Luxembourg

Belair, Luxembourg City

7,213

29

Iceland

Rimar, Reykjavik

5,738

30

Cyprus

Agios Nektarios, Limassol

5,439

Taken together, it’s striking how many were built within the same narrow window of time. Among Western European countries, only Greece and Iceland built their densest areas after the First World War. In Greece’s case, the development still cleaves closely to a pre-war model (tenements built without setback on narrow streets). Meanwhile, just one country’s densest square kilometer predates the mid-19th century: Italy’s, where parts of Naples’s densely populated Pendino stretch back beyond the 17thcentury. That leaves the rest originating between 1850 and 1914.

Eight of these densest areas stem from this period—all of which were initially built for the working and lower middle class. Further down the list, areas that are now somewhat less dense—such as Helsinki’s once disreputable but now highly desirable Punavuori or Budapest’s District 8—date from the same era, but have had their populations substantially thinned by post-World War II construction. Districts of taller, modernist towers and slabs built at greater intervals may crop up more frequently in the former Eastern bloc, but only in Bulgaria (in Belite Brezi, Sofia) is that district especially densely populated by pan-continental standards.

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What caused this sudden outburst of density in the late 19th and early 20th centuries? According to Andreas Schulze Bäing, lecturer in urban planning at the University of Manchester, these districts’ layouts reflect a particular moment in European history. As Europe’s urban population swelled with industrialization, cities started to grow beyond the boundaries of their medieval walls. New outer-ring districts were built to accommodate new armies of workers. This era famously gave us huge avenues like Paris’s concentric circles of boulevards and Vienna’s Ringstrasse. These grand promenades were laid out on the site of former fortifications that had been rendered obsolete by changes in warfare. (The term boulevard has the same root as “bulwark,” meaning a defensive rampart, or the space kept clear within one.)

Huge new tenement districts were another major product of this industrial push. Advances in construction technology made it cheaper and easier to build buildings of considerable height, compared to previous eras. After centuries of being strangled by ramparts and limited by a lack of machinery, Europe began building upwards.

The flexibility of industrial tenements has ensured their popularity, even as residents’ needs have changed.

But cities were still hampered by rudimentary transit systems. Subway and traffic management were still in their infancy, so workers still needed to live within walking distance of work. Conditions for new lower-income housing thus set in across the continent. These new neighborhoods had to be close to industrial areas or city cores, they had to have a large number of units and—with few exceptions—they had to be cheap.

The results of these pressures can be seen in this aerial view of Europe’s single densest square kilometer, located in L’Hospitalet de Llobregat, a textile-producing town that swelled to join Barcelona in the late 19th century. Spain’s cities have always been (and continue to be) very densely populated, possibly reflecting both a martial influence that lingered after the expulsion of Spain’s Moors and the influence of a Moorish planning style that favored narrow streets as a way of reducing summer temperatures. The sheer density of the square below is still extraordinary: With 53,119 residents, this square kilometer is about twice as dense as Manhattan overall.

The streets here are so narrow that they feature in the image above as small veins of shade running through a thick canopy of red-tiled roofs. Equally striking is how filled-in each block appears, lit with only the narrowest of courtyards and light wells. In a climate with hot summers, this lack of sunlight exposure has some advantages in keeping interiors cooler.

Spanish cities’ extreme density is exceptional—many areas of Greater Barcelona approach this kind of density, which also comes close to being matched in less topographically-confined Madrid. But this tight street plan is not an exclusively Spanish phenomenon. Take a look at the most densely populated square kilometer of the Netherlands, located in Amsterdam’s De Pijp neighborhood.

Built on partly reclaimed land following a plan launched in 1876, De Pijp’s layout allowed only for the narrowest slivers of road between tenement blocks, which were built with the cheapest of materials and not uncommonly divided into single-aspect, one-room apartments that housed entire families of new arrivals from the Dutch countryside. Now the area looks singularly pretty for a former slum—especially thanks to its park, whose site was originally left clear for a railway station that never came to be. It’s only from above that you realize the planners’ true parsimony in leaving room for public space.

This narrowness of street plan isn’t in itself ubiquitous. Densely populated areas in many northern European cities have notably broader streets. Beyond the grand facades that flank the wider roadways, you’ll usually find warrens of heavily populated, roughly built courtyards.

Look, for example, at Poland’s densest square kilometer—located in the northwestern city of Szczecin. The population of this major port and industrial center increased almost eight times between 1815 and 1900. Szczecin (then German Stettin) expanded substantially after its city walls were demolished in 1873, following a design by the same person responsible for Paris’s 19th century transformation, Baron Haussmann.

Explore this area on Google Street View and it gives the impression of generous expansiveness—naturally more Prussian than Parisian, with battered but grand tenements flanking reasonably wide streets. Look at the same area from above, and you see that each block has a tightly packed interior, and many apartments face onto narrow slivers of courtyard. This harsh contrast of opulent facades on often rough-shod buildings was a major spur pushing the light-filled, facade-less innovations of the modernist movement.

A view of the Czech Republic’s square kilometer, in the inner Prague district of Žižkov, shows a similar pattern. Heavily built-up after the demolition of the city walls (in 1874), Žižkov from above suggests greater spaciousness, with some trees finding space to grow in the back courtyards. Even here, however, the overall pattern would have been one of overcrowding, with an average of 56 residents per building in the area in 1890, and many small workshops occupying the building’s back yards.

Despite these repeating patterns, there’s one heavily industrialized Western European country that remains exception: the U.K.

While other countries built relatively tall tenement blocks (a pattern repeated at lower heights in Scotland), England’s and Wales’s industrial cities spread out with a sprawling skirt of low-rise row houses. This is partly because Britain’s industrial revolution started so early. With much of the U.K.’s urban expansion occurring in the late 18th and early 19th centuries, residential patterns were largely set before mechanization made it easier to build the taller buildings found in continental cities.

Britain’s most densely populated square kilometer—in London’s Maida Vale—still resembles what we’ve seen in cities on the continent. Its high density is nonetheless atypical of London. And, as the size of the gardens in the image reveals, so were its residents, who were generally wealthier than what was usual for the densest districts elsewhere. Indeed, the few areas of London where Victorian residential buildings are notably taller, such as Belgravia, were mainly reserved for the rich.

The narrow, heavily built street plans of late 19th century continental districts are efficient and sustainable when seen through today’s eyes, but were reviled with some justification during their construction period. You can sense the suspicion and hostility to such areas in the very German name for tenements: Mietskaserne or “rental barracks.” These were grim places of regimented living where the Hinterhof, or back courtyard, became a synonym for poverty and want.

“In the period after these industrial tenements were constructed, it was not uncommon for a worker to simply rent the right to sleep in a bed just for a portion of the day,” Schulze Bäing told CityLab. “You could have a single bed rented out in three daily shifts.” The process of thinning these areas out and adding amenities was a slow one that unfolded across the 20th century. That process, Schulze Bäing notes, has only recently ended. “In Berlin, right up until the 1980s and ‘90s, many Berlin tenements shared only one toilet per floor.”

It’s thus no coincidence that Berlin’s Neukölln, which contains Germany’s densest square kilometer, only really began the process of gentrification after 2000. If you look at the image below, you can get an idea of why. Tenements rise like fortress walls directly from the sidewalk. The streets’ lack of green space would have mattered even more in the era when every home was heated by a smoke belching coal stove. The apparent sense of spaciousness, meanwhile, is largely a modern characteristic that developed in the late 20th century, as new housing construction elsewhere thinned the areas’s population.

Such areas possess a few decorative charms—such as art nouveau masks in plaster over their doorways, or occasional turret-like roofs tacked on to corners—but these catalog-bought embellishments are just surface add-ons. It makes some sense that contemporary Berlin gentrifiers turned to other tenement districts with more greenery and architectural embellishment before ultimately setting their sites on grimy, “authentic” Neukölln after the millennium. Check the area out on Street View and it’s pleasant enough, but it doesn’t take a great leap of imagination to understand why 50 years ago, people often wanted something more open and informally laid out.

The sprawl of post-war suburbs and 20th century districts of high-rise towers were indeed a reaction against such conditions. Modernist towers and slabs developed as alternatives, often located near older tenement districts. They not only introduced more light and green space, but also broke down the distinction between a building’s back and front—a distinction that carried class implications. These older, denser areas only became desirable over the course of many laborious decades, during which basic amenities such as bathrooms were installed and the population thinned out somewhat.

A partial view of Žižkov, Prague, from the city’s television tower. (AP/Petr David Josek)

So why, given their early reputation for overcrowding and poverty, have such areas proved enduringly popular as places to live? Partly because the more sprawling suburbs have proved to be inefficient and decidedly un-magnetic places to live. Inner-city tenements were often raw barracks, but their facades still have an undeniable charm that can actually be enhanced by grime. Their closeness to amenities, city cores and transit ultimately makes them more livable. Above all, the flexibility of industrial tenements has ensured their popularity, even as residents’ needs have changed.

“One reason why areas like this have such low vacancy is that the built environment is very adaptable,” Schulze Bäing says. “In the flats, the rooms are more or less all the same, unlike in modernist housing where each space has a tailored, specialized function. Such flats may not have been designed with that flexibility in mind, but they can respond easily to changing demands—they can be offices or shops or homes.”

This has helped to make such areas hugely popular to live in, and perhaps masked some of their historic perception as places to escape. Does that mean we should condemn their planning and avoid their influence? Not in the slightest. Europe’s most densely populated areas had a long, slow journey to becoming generally desirable. That journey involved residents’ living conditions improving through major social and technological change. And it can’t be forgotten that certain areas only became desirable as they became inaccessible or unaffordable for the lower-income residents they were originally built for. In contemporary planning, we should reflect that the models we espouse today required decades of adaptation and modification before reaching the form that we aspire to now.

About the Author

Feargus O'Sullivan is a contributing writer to CityLab, covering Europe. His writing focuses on housing, gentrification and social change, infrastructure, urban policy, and national cultures. He has previously contributed to The Guardian, The Times, The Financial Times, and Next City, among other publications.